1. Field of the Invention
The present invention relates to couplers for use with pickup drawbars on work vehicles.
2. Description of the Related Art
Most farm, industrial and other work vehicles are provided with a drawbar for towing implements, trailers and the like. Such drawbars usually are able to swing somewhat from side to side and sometimes are longitudinally adjustable as well, e.g., as taught in U.S. Pat. No. 3,795,415 (Koch et al.). Pickup drawbars which are vertically movable under power sometimes are provided where the implements to be towed are heavy enough that it is difficult to manually lift the implement tongue onto the drawbar. Such pickup drawbars may be straight, as taught in U.S. Pat. No. 3,791,456 (Koch), but often are provided with a hook end, as taught in U.S. Pat. No. 3,863,955 (Muncke et al.).
Whatever the drawbar structure, some coupling mechanism must be provided to attach the implement to the drawbar. There is a wide variety of such mechanisms, the most common of which is a simple drop pin. With such a structure, either the drawbar is provided with two flanges which extend over a ring ended implement tongue or the implement tongue is provided with two flanges which extend over a flat drawbar. A pin then is dropped through holes in the drawbar and implement tongue, and held in place by a cotter pin or spring, as shown in U.S. Pat. No. 4,008,905 (Soteropulos et al.), or by some sort of horizontally pivotal plate, as shown in U.S. Pat. No. 3,794,357 (Frye). U.S. Pat. No. 1,145,026 (Lechtenberg) teaches a further alternative using a spring biased hook rather than a pin. With any of these constructions, excess clearance around the pin or hook allows some degree of movement or "slop" between the implement tongue and the drawbar.
Sometimes, as when a PTO shaft is to be connected between a tractor and an implement, this slop must be avoided. A ball coupler of some form then typically is used. The most common ball couplers provide a ball on the drawbar and a mechanism on the implement tongue to hold the ball. Pivotal movement of the implement tongue around the ball still can occur, but longitudinal movement between the drawbar and the implement tongue is prevented. U.S. Pat. Nos. 3,827,724 (Ackley), 4,008,906 (Schafer et al.) and 4,434,996 (Wallace) provide examples of such ball hitches. In all three of these references, a clamp mechanism of some form is provided to hold the implement tongue on the ball.
Alternatively, the implement tongue can be provided with a captured ball hitch, in which a ball is movably captured within a ring hitch. A hole is provided through the ball, and the hitch can be attached to a drawbar by putting a pin through the hole, as shown in the Soteropulos et al. reference.
Each of the aforementioned coupling techniques has certain disadvantages. Drop in pins and spring-biased hooks do not work well with a pickup drawbar since the implement tongue can simply slide off the drawbar before the pin or hook is dropped in place. A pre-mounted pin such as shown by Soteropulos et al. overcomes this problem, but has the remaining problem that a high amount of stress is placed on the cotter pin if the angle between the work vehicle and the implement is such that the implement tongue is lifted upwards from the drawbar. Finally, the clamp mechanisms used with conventional ball couplers typically have a relatively high number of parts, increasing their complexity.